package iptables

import (
	"errors"
	"fmt"
	"net"
	"os/exec"
	"strconv"
	"strings"
)

type Action string

const (
	Add    Action = "-A"
	Delete Action = "-D"
)

var (
	ErrIptablesNotFound = errors.New("Iptables not found")
	nat                 = []string{"-t", "nat"}
)

type Chain struct {
	Name   string
	Bridge string
}

func NewChain(name, bridge string) (*Chain, error) {
	if err := Raw("-t", "nat", "-N", name); err != nil {
		return nil, err
	}
	chain := &Chain{
		Name:   name,
		Bridge: bridge,
	}

	if err := chain.Prerouting(Add, "-m", "addrtype", "--dst-type", "LOCAL"); err != nil {
		return nil, fmt.Errorf("Failed to inject docker in PREROUTING chain: %s", err)
	}
	if err := chain.Output(Add, "-m", "addrtype", "--dst-type", "LOCAL", "!", "--dst", "127.0.0.0/8"); err != nil {
		return nil, fmt.Errorf("Failed to inject docker in OUTPUT chain: %s", err)
	}
	return chain, nil
}

func RemoveExistingChain(name string) error {
	chain := &Chain{
		Name: name,
	}
	return chain.Remove()
}

func (c *Chain) Forward(action Action, ip net.IP, port int, proto, dest_addr string, dest_port int) error {
	return Raw("-t", "nat", fmt.Sprint(action), c.Name,
		"-p", proto,
		"-d", ip.String(),
		"--dport", strconv.Itoa(port),
		"!", "-i", c.Bridge,
		"-j", "DNAT",
		"--to-destination", net.JoinHostPort(dest_addr, strconv.Itoa(dest_port)))
}

func (c *Chain) Prerouting(action Action, args ...string) error {
	a := append(nat, fmt.Sprint(action), "PREROUTING")
	if len(args) > 0 {
		a = append(a, args...)
	}
	return Raw(append(a, "-j", c.Name)...)
}

func (c *Chain) Output(action Action, args ...string) error {
	a := append(nat, fmt.Sprint(action), "OUTPUT")
	if len(args) > 0 {
		a = append(a, args...)
	}
	return Raw(append(a, "-j", c.Name)...)
}

func (c *Chain) Remove() error {
	// Ignore errors - This could mean the chains were never set up
	c.Prerouting(Delete, "-m", "addrtype", "--dst-type", "LOCAL")
	c.Output(Delete, "-m", "addrtype", "--dst-type", "LOCAL", "!", "--dst", "127.0.0.0/8")
	c.Output(Delete, "-m", "addrtype", "--dst-type", "LOCAL") // Created in versions <= 0.1.6

	c.Prerouting(Delete)
	c.Output(Delete)

	Raw("-t", "nat", "-F", c.Name)
	Raw("-t", "nat", "-X", c.Name)

	return nil
}

// Check if an existing rule exists
func Exists(args ...string) bool {
	return Raw(append([]string{"-C"}, args...)...) == nil
}

func Raw(args ...string) error {
	path, err := exec.LookPath("iptables")
	if err != nil {
		return ErrIptablesNotFound
	}
	if err := exec.Command(path, args...).Run(); err != nil {
		return fmt.Errorf("iptables failed: iptables %v", strings.Join(args, " "))
	}
	return nil

}